The present invention relates generally to building components and, more particularly, but not exclusively, to building components for roofing, in the form of inflatable cushions.
Inflatable cushions comprise two or more layers of a plastic foil material such as ETFE (ethylene tetra flouro ethylene) inflated with low pressure air. The ETFE foil cushion is restrained in a perimeter frame usually manufactured from extruded aluminium, which in turn is fixed to a support structure. As the ETFE foil cushion is inflated, the ETFE is put under tension and forms a tight drum like skin. ETFE foil cushions are sold under a number of trade names, for example “Texlon.”
ETFE cushions of this kind are fixed to a support structure to form a cladding and are used to enclose atria or other enclosed spaces to provide a transparent or translucent roof or facade to the enclosure, as an alternative to and in a similar way to glass. A number of buildings have been built using this technology most notably the Eden project in Cornwall, England.
Whenever a space is enclosed by a cladding system due consideration needs to be given to the effects of a fire should it break out in the building. In these circumstances, smoke and other products of combustion must be ventilated from the enclosure to prevent injury to the occupants and property. In some specialist buildings, other noxious fumes may also need to be ventilated from the enclosure to prevent injury to the occupants and property. In some specialist buildings, other noxious fumes may also need to be ventilated to atmosphere.
To ventilate noxious fumes to atmosphere, two methods are primarily utilized. Firstly, the smoke, and/or fumes can be extracted by a mechanical extraction system usually consisting of fire-rated duct work and extraction fans. Alternatively, the smoke and/or fumes can be extracted by opening part of the roof or building facade and allowing the smoke to ventilate to atmosphere through the action of convection and/or wind.
ETFE foil cushions can be used to ventilate smoke and/or fumes to the atmosphere in much the same ways as other cladding systems in that they can be fixed to a frame which opens automatically through a mechanical device in the event of fire. In addition, ETFE is a thermo-plastic material and therefore has the innate property of failing if the temperature reaches approximately 200° C., as the material loses its tensile properties as its temperature increases. When the cushion fails, it allows smoke and/or fumes to ventilate naturally to the atmosphere.
The above methods suffer from a number of draw backs. The mechanical extraction approach is expensive and requires fire-rated machinery, regular maintenance and testing. Natural extraction requires expensive opening frames, which are complex to render, weather and watertight. They do not look the same as the adjacent cladding as they require a secondary opening frame, and mechanical operating parts which themselves require regular maintenance and testing. The failure of the ETFE due to high temperature does not occur if the building fire is located some way away from the ETFE, as the ETFE is not sufficiently heated by smoke and/or fumes to fail.